One type of a steering is known from EP 0 244 418 B1. Such steerings are particularly used in driven machines, for example mobile agricultural equipment. The steering unit activated by the steering initiator, for example a steering handwheel, is used to permit a driver to steer the vehicle. This mode of operation is particularly useful in the road traffic. The auxiliary-force activated steering valve can be used for automatic steering of the vehicle, for example along a path defined from the outside.
In a steering unit, which has feedback properties, it is not absolutely necessary to have a mechanical connection between the steered wheels and the steering initiator, for example the steering handwheel. However, a hydraulic connection is continuously available from the steering motor to the steering unit, so that forces, which act upon the wheels steered by means of the steering motor, can also be felt on the steering handwheel. As soon as the steered wheels are loaded from the outside, pressures are generated in the steering motor, which propagate up to the steering unit thus reaching the measuring motor, which again transfer them to the steering handwheel.
In a steering having a steering unit with feedback properties, it can therefore frequently be seen that the steering initiator moves, when the vehicle is steered by means of the auxiliary-force activated steering valve. When the steering initiator exists in the form of a steering handwheel, this steering handwheel can turn at an activation of the steering by the steering valve, which can be very disturbing for the driver.
Therefore, a change-over valve has been provided in the known steering, which in a first position connects the working connection arrangement with the steering motor and in a second position connects the working connections with each other and separates them from the steering motor. In this case, the steering of the vehicle takes place merely via the steering valve.
This, in fact, prevents a feedback from the steering motor to the steering handwheel, when the vehicle is steered via the steering valve. However, it is not possible for the driver of the vehicle to intervene in the steering behaviour of the vehicle via the steering handwheel, when this is necessary or desired. This can lead to dangerous situations.